How to temporarily close access to the database?

Question

PHP

I have a table with points.
How to make it so that while one removes / replenishes points, the other person cannot do the same?
Example: there are points-A (points) and points-B (tiles)
They can be converted into each other. Both tables are limited in number (max points = 100, max tiles = 50000) throughout the database.
How to make it so that while one converts tiles to points, no one can do this (so that it does not happen that both exchange points and they suddenly become -10)?

Answer 1

Locks in MySQL on Habré.
In short:

LOCK TABLES tiles, points WRITE;

-- тут конвертируем одно в другое

UNLOCK TABLES;

Answer 2

Need to use transactions